The decision by the European Space Agency (ESA) to proceed with next year’s planned launch of the Sentinel 1A Earth observation satellite is welcome news, but the related funding issue that put the launch in doubt in the first place has yet to be resolved.

ESA threatened to ground the initial satellites in the Global Monitoring for Environment and Security (GMES) constellation after the European Union (EU) wavered on its commitment to fund the program. GMES as currently structured consists of three virtually identical rounds of three Sentinel spacecraft. ESA is prime contractor on the program and is funding satellite development and launch; the EU is responsible for operating and maintaining the constellation in orbit.

GMES managers had asked for 5.8 billion euros ($7.3 billion) over the EU’s seven-year budget period that begins in 2014 and is funded through mandatory contributions from member states. But the EU Commission recommended last year that the program instead be funded from voluntary contributions by individual members, a recipe for trouble in any number of forms. The commission’s stated rationale, that GMES was susceptible to cost growth, was dubious given that Sentinel development by mid-2011 had advanced past the stage where satellite projects typically hit inflationary technical snags.

ESA was justified in holding the initial Sentinel launches hostage pending assurances that the EU would finance GMES beyond 2014 — there’s little point in going to the trouble and expense of launching a satellite whose operations budget runs out in less than a year. Whether or not it was intended as such, ESA’s threat was an effective way of drawing high-level attention to a potential showstopper on a program in which European nations had already invested more than 3 billion euros.

For whatever reason, EU ministers during a June meeting adopted a proposal by Denmark, the current holder of the union’s six-month rotating presidency, to accommodate GMES within the EU’s 1.3 trillion euro budget for 2014-2020. ESA subsequently agreed to go ahead with the Sentinel 1A launch, a move that was prompted at least in part by the unexpected loss this past spring of its flagship Envisat environmental satellite, which like Sentinel 1A was equipped to collect radar imagery.

But serious questions remain about the level of EU funding that can be expected for GMES starting in 2014. The Danish proposal not only omitted a specific funding figure for GMES, it also lumped the program together with the Galileo satellite navigation system and the International Thermonuclear Experimental Reactor project.

The problem with that grouping is that cost growth on one program could erode the budget of another, and the nuclear reactor is a mega-scale effort with enormous technical challenges that has already seen substantial cost increases. Additional cost growth seems likely on a program of this complexity and, given the reactor’s current price tag — the EU’s share is estimated at nearly 7 billion euros — could take a substantial bite out of the GMES and Galileo budgets.

ESA’s member governments must continue to press the EU for a budget that assures GMES operations through 2020; if they have to hold the second and third Sentinel satellites hostage to get the point across, so be it. Too much has been invested in this program, and the mission is too important, to subject its future to the vagaries of multiple annual budget processes in economically uncertain times.